Of course, that only raises more questions. I wasn’t immediately able to get further information this afternoon about why Microsoft submitted the filing, or what product it might be related to, but I’ll follow up with more info if I do.

Microsoft Corp., Google Inc. and four other technology companies plan to submit a prototype of a new handheld device to U.S. regulators for testing, as they press the government to free up airwaves for wireless Internet access.

Microsoft is developing the prototype, which the coalition will submit to the Federal Communications Commission’s Office of Engineering and Technology, according to a Feb. 5 letter the companies filed with the FCC. The device would “provide consumer broadband access and networking,” the filing said.

The commission is considering whether to let companies offer wireless Internet access on handheld devices that would use vacant television airwaves, known as white spaces. A law enacted last year requires TV stations to convert to digital technology by February 2009, freeing up their old airwaves.

Update III: Here’s a copy of the actual letter to the FCC that caused the hubbub: PDF, 5 pages. Note that it’s submitted “on behalf of a coalition that includes Dell, Google, Hewlett-Packard, Intel, Microsoft and Philips,” and doesn’t allude to Zune.

Who knows, maybe this particular wireless technology could be used in a Zune device somewhere down the road, and maybe even in a Zune phone. But given all the consumer-electronics technologies Microsoft is involved in, it would be quite a leap to construe the letter alone as confirmation of any specific Zune plans.